报告题目：Secrets of swimming in sand

报 告 人：丁阳，Aerospace and Mechanical Engineering, University of Southern California，USA

报告时间：12月9日（周一）下午3:00

报告地点：物理系三楼报告厅

报告摘要：Locomotion within granular media like sand, soil and debris that display both solid and fluid-like behavior is challenging and not well understood. Here I summarize my modeling efforts to understand the swimming of the sandfish lizard in sand. High speed x-ray imaging showed that the 10 cm-long sandfish swims at 2 body-lengths/sec within sand by propagating an undulatory traveling wave down the body. To predict the sandfish swimming speed in sand, we developed an empirical resistive force model by measuring drag force on a small cylinder oriented at different angles relative to the displacement direction and summing these forces over the animal movement profile. The model correctly predicts the animal's wave efficiency (ratio of forward speed to wave speed) as approximately 0.5. The model also explains the muscle activation pattern observed on sandfish and solved a long-standing puzzle of undulatory swimmers. The empirical model agrees with a more detailed numerical simulation: a multi-segment model of the sandfish coupled to a multi-particle discrete element method (DEM) simulation of the granular medium.